From the study of the human digestive system, it has been found that a huge variety of nutritional substances are obtained by breaking down and digesting the food in the gastrointestinal tract. The gastrointestinal tract is an important route by which the food is digested and absorbed. With regard to absorption, the nutritional substances, such as glucose, amino acids, vitamins and other smaller molecules are absorbed along the entire tract, either by diffusion or by specialized transport processes. Instead of moving freely across the intestinal membrane to the blood stream or lymph, most of these nutritional substances are transported by a tightly regulated mechanism. Based on current understanding in cell biology and physiology, the nutritional substances are transported across the cells with specific transport proteins and channels anchored on the cell membrane.
In the example of glucose transportation, almost all of the cells have a carrier-mediated mechanism for the transport of glucose from blood. For most cells, this transport occurs by facilitated diffusion using one or more of the glucose transporters (GLUT) in a family of facilitated glucose transporters. In these cases, net glucose transport occurs as a result of an inwardly directed chemical gradient for glucose. In a few cell types (e.g. those of intestinal mucosa and renal proximal tubule), uptake of glucose from an extracellular solution can occur against a gradient of glucose in a so-called active transport mechanism, thereby permitting net absorption of glucose from a tissue compartment whose glucose concentration may be lower than that of the blood. There are two ways in which a flow of energy can be coupled to transporters. The primary active transport requires energy be provided by adenosine triphophatase (ATPase). The secondary active transport provides energy from the flow of ions from an area of higher concentration to one of lower concentration.
According to the secondary active transport model described above, Na+ binds to transport protein on the luminal side of the cell causing conformational change of the transport protein, which opens the binding site for glucose. Then, glucose binds to the transport protein. The transport protein that is bound with both Na+ and glucose is subjected to further conformational change to allow entry of glucose and Na+ into the cells. This active transport of glucose involves a direct physical coupling of flows of Na+ and glucose, with the energy of the process being derived from the inwardly directed gradient for Na+. Since the transport event includes a net movement of charge (the cationic Na+ ion with the non-electrolyte glucose), the driving force for this uptake includes both the chemical gradient for Na+ and the potential difference across the membrane. As the glucose gradually accumulates in the cell, it is subsequently transported out to the blood vessel via a glucose concentration gradient by facilitated diffusion. Similarly, other nutritional substances may be absorbed with the transport mechanism described above.
Astragalus root (Radix Astragali) has been used as a traditional Chinese medicine that mainly serves to invigorate the function of the spleen and increase stamina and endurance. Astragalus root (Radix Astragali) was found to enhance the immune system and help the human body resist virus infections, particularly in the lungs, by increasing production of interferon, an immune factor that inhibits viral growth. Astragalus root has been used as an adjuvant therapy in the treatment of colds and influenza. Radix Astragali was also reported to have effects on cardiovascular activity. Alcohol extracts of Radix Astragali enhanced both the contractility and contraction amplitude of isolated frog or toad hearts. Furthermore, astragalosides isolated from Radix Astragali have been reported to exert a positive inotropic effect on isolated rat hearts.
However, Astragalus membranaceus var. mongholicus has not been implied in regulating nutrient absorption and transportation. None of the study or research has focused on regulating the nutrient absorption using saponin compounds purified from Chinese herbal medicines, particularly Astragalus membranaceus var. mongholicus. 